As the aerial storage densities of disc drives increases, the distance between adjacent concentric tracks decreases. Decreasing track spacing increases the difficulty of precisely positioning the transducing head over a selected track on the medium. Most disc drives employ a voice coil motor (VCM) that rotates the actuator assembly of the disc drive to position the head relative to the track. However, resonant modes of vibration in the actuator make it increasingly difficult to accurately follow the tracks, particularly as track spacing decreases. Consequently, dual-stage actuation has been employed using the VCM to coarsely position the arm and transducer relative to a selected track, and using a microactuator to finely position the transducer relative to the arm to thereby finely position the transducer relative to the selected track.
The microactuator comprises a stator and a rotor. In one form, commonly referred to as a slider level microactuator, the stator is mounted to the suspension, and the rotor supports the slider. Other forms of microactuator include arm level microactuators in which both the stator and rotor are embedded in the arm to deform the arm to finely position the transducer, and suspension level microactuators in which the stator is mounted to the arm and the rotor supports the suspension. Slider level microactuators are of minimal mass and can be modeled as single degree of freedom spring mass damper systems over a wide range of frequencies. Hence, slider based microactuators are easily adapted for use in disc drives. While the present invention will be described in relation to slider level microactuators, the principles of the present invention can be adapted to arm level and suspension level microactuators as well.
As track densities continue to increase, the fly height, and particularly fly height variations, of the slider become increasingly important. More particularly, the transducers must be increasingly smaller (narrower) as track spacing increases and track widths decrease. To accommodate signal and noise issues associated with smaller track widths, the slider and transducer must “fly” at a lower fly height and with less fly height variation. Accordingly, there is an increasing need for maintaining a smaller and a constant air gap between the slider and the disc.
Currently, the air gap is maintained passively through the use of the suspension and aerodynamic design of the slider forming the air bearing. Requirements for increased aerial densities and disc speeds and decreased fly heights render passive control of the fly height increasingly difficult and less reliable. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.